This invention relates to an improved drive shaft, such as is used in transmitting power from an automotive engine to the wheels, and more particularly, to a drive shaft of the same size and at least of the same strength as a conventional drive shaft, but of considerably lighter weight.
Drive shafts that are used in automotive vehicles for transmitting the engine rotary power to the wheels, typically, are formed of a solid, elongated, metal shaft having coupling formations formed on its opposite ends. These may comprise splines or other suitable couplings for connecting the ends of the shaft to the related engine and wheel connecting parts. Conventional drive shafts, that are used for front end drive vehicles, may be in the range of about 12 inches to about 36 inches, although the lengths vary considerably. These shafts are usually manufactured by forging and machining techniques and are relatively heavy. By way of example, an approximately 27 inch long shaft of about 1 inch diameter weighs about 5 pounds.
In recent times, in connection with fuel saving measures, vehicle manufacturers have endeavored to lighten the weight of various vehicle components. In the case of the power transmission shafts, reducing the weight is difficult because of the strength requirements and the manufacturing techniques used. Attempts have been made to drill through the center of such a shaft, so that the shaft is hollow, to reduce the weight, but this is relatively expensive and tends to weaken the shaft. Thus, there is a need to provide a manufacturing method to produce hollow, light weight drive shafts which maintain the strength requirements normally associated with solid shafts.
One manufacturing method for producing elongated tubes is cold forming extrusion. This manufacturing process is described in my U.S. Pat. No. 3,837,205 issued Sept. 24, 1974 for a "Process for Cold Forming a Metal Tube With Inwardly Thickened End", U.S. Pat. No. 3,886,649 issued Jun. 3, 1975 for a "Process for Cold Forming a Metal Tube With An Inwardly Thickened End", U.S. Pat. No. 4,277,969 issued Jul. 14, 1981 for a "Method for Cold Forming Tubes Within Interior Thicker Wall Sections" and U.S. Pat. No. 4,292,831 issued Oct. 6, 1981 for a "Process for Extruding Metal Tube with Inwardly Thickened End Portions". In addition, a similar process is disclosed in my copending application, U.S. patent application Ser. No. 07/490,286, filed Mar. 8, 1990, now U.S. Pat. No. 4,991,451 and relating to a Steering Gear Rack Type Device. The invention herein is concerned with adapting the cold forming extrusion process for manufacturing tubular drive shafts having central sections formed with thinner walls than the end sections for reducing the weight of the article while maintaining its required performance strength and structural characteristics.